This invention relates to a chair preferably used in an office or a home.
As a general structure to constitute a seat and a back for this kind of chair there is a structure wherein a seat is formed with a shell construction to be a seat shell, a back is formed with a shell construction to be a back shell and the seat shell is supported by a seat support and the back shell is supported by a back support rod as described in the patent document 1, or a structure comprising a shell into which the seat and the back are integrally formed as described in the patent document 2.
(Patent document 1) Japan patent laid open number 8-10084
(Patent document 2) Japan patent laid open number 11-266957
A cushion material is mounted on the back or the seat for either of the above-mentioned chairs. In addition, there is a chair having a structure wherein an opening arranged at the seat or the back is covered with a coating cloth such as a mesh member with tension so as to improve a support feeling. In case of adopting this kind of coating cloth, in stead of a shell structure, a frame structure having a back frame or a seat frame provided with an opening is necessary in order to secure a margin for allowing the coating cloth to bow. However, if the arrangement described in the patent document 1 is made with the frame structure having a back frame and a seat frame, the back frame and the seat frame, each of which is separated, have to be connected by the use of a connecting member, resulting in a load concentrating on a joint and the joint is unjointed in a short time. As a result, the chair becomes undurable. Although the arrangement described in the patent document 2 is such that the seat and the back are integrally formed, a load concentrates on a boundary part between the seat and the back, resulting in causing a crack slowly.
An object of the present claimed invention is to provide a chair having a frame structure that is effective for securing a required strength without needless structure to reinforce the strength.